This invention relates to apparatus and methods for the molding of glass, such as glass molding presses and methods for the formation of television and computer faceplates. More particularly, this invention relates to the mechanisms and methods by which such presses are controlled.
A desirable machine for the production of glass products from gobs includes a vertically reciprocable ram or plunger which is movable to a molding position with an underlying mold. Glass is introduced to the mold as a gob while the ram is raised. The ram is then extended downward to the gob and mold, pressing the glass against the mold. Once the glass solidifies sufficiently, the ram is raised. A table carrying the mold is indexed to carry the mold to new workstations, while successive molds are successively indexed under the ram.
Increased speeds of production are highly desirable. In 1976, Lynch Corporation, then of Anderson, Ind., introduced a control system for operating the ram of glass molding machines which substantially advanced the art of such machines. This control, disclosed in U.S. Pat. No. 3,953,187 issued on Apr. 27, 1976, provided for rapid lowering of the ram to the mold, and numerous other advantages. Hydraulic circuitry was employed, and production speed was substantially improved.
In 1988, Owens-Illinois Television Products, Inc., of Toledo, Ohio, now called Techneglas, patented and disclosed another control. This control maintained the Lynch concept of rapid lowering of the ram to the mold. It added ram movement causing a spike of ram pressure as the ram contacted the gob in the mold. This ram pressure spike was employed as a signal to cause a controller to reduce pressure linearly to a final pressing pressure. The spike, linear reduction, and final pressing pressure are as shown along the "Down Ram Pressure" line of FIG. 2 of U.S. Pat. No. 4,723,976, in the region of time from 4.8 to 7.5 seconds, as charted. Oilgear Company of Milwaukee, Wis., was the recognized supplier of the servo control of the system.
U.S. Pat. Nos. 3,953,187 and 4,723,976 are incorporated by reference. U.S. Pat. No. 4,554,001 issued Nov. 19, 1985 is also incorporated by reference.